1. Field of the Invention
The present invention relates generally to a container for growing plants, and, more particularly, to a container for growing plants such as trees and shrubs for transplanting.
2. Description of the Prior Art
Plants, such as trees and shrubs, which are intended to be transplanted are commonly grown above ground in containers. Such containerized plants can be grown at a faster rate than those grown in the ground, they are more easily tended, and because the roots of the plants are not severed when the plants are transplanted, transplanting is more often successfully accomplished.
Various types of containers have been used for growing plants, by retaining and bounding the soil and roots of plants prior to transplanting. For example, metal cans and cylindrical plastic containers with holes in the bottoms were among the first plant growing containers used.
When a plant seed germinates the first or primary root, often referred to as a taproot, plunges downward in an effort to secure the new plant in place and to secure access to moisture and nutrients. The taproot on some plant species extends only a few inches while in others the taproot extends 10 feet or more if environmental conditions in the soil allow.
A smooth-walled conventional container for growing transplantable plants is illustrated in FIG. 1 and generally designated by the numeral 1. The container 1 is comprised of a cylindrical body having a continuous arcuate sidewall 3 for bounding and retaining a transplantable plant 5 having taproot 7 in a volume of soil or other growth medium 9. The taproot 7 grows until it reaches the bottom of the container, and then changes direction in response to impacting the container while continuing to grow until circling becomes physically restricting to growth.
Once the taproot stops growing or extending, the apical dominance of its root tip is lost and the development of some secondary lateral rooting occurs. The secondary roots are much less influenced by gravity and extend more horizontally, although still partially downwardly, in direction. When such roots contact the sides of a plant container, unless trapped or air-pruned they turn and grow downwardly in a spiral path along the sides to the bottom of the container where they continue to grow in a circular pattern. As further roots form off the secondary roots, called tertiary roots, these roots have an even greater horizontal tendency, but still retain a modest downward tendency and often end up in circular patterns at the bottom of a smooth inner-walled, conventional container as well.
Plants that are transplanted with root growth that extends downwardly and concentrated at the bottom of a container, as described above, suffer because the roots provide little or no lateral anchorage of the plant, and the tips of the roots are at a depth in the soil where aeration is less favorable. In addition, the downwardly-directed roots are intermingled with each other and as they increase in diameter with age, they exert pressure on one another that can restrict the normal flow of water and nutrients through the roots.
Cylindrical containers having holes in the sides to inhibit such concentrated spiral and circular root growth have been utilized in the art. The side holes or openings function to cause air-pruning of the roots, a phenomenon in which the growth of a root stops when the root extends into the vicinity of an opening that is exposed to the atmosphere, essentially because the atmosphere cannot provide the requisite moisture necessary for continued growth. While the use of cylindrical containers with side holes reduces the incidence of spiraled and circled roots, some spiraling and circling can still take place because the roots are not positively directed towards the side holes and can evade the side holes by ricocheting off the inner surfaces of the container sides between the holes.
Transplantable landscape plants have also been grown in square, bottomless containers placed on wire screens whereby roots reaching the bottom of the container are air-pruned. Most of the resulting root tips end up at the bottom of such containers, reducing lateral anchorage. Furthermore, the requirement of placing the containers on wire screen surfaces generally makes the practice cumbersome and uneconomical.
Other containers have been developed (see, e.g., U.S. Pat. No. 5,099,607 issued on Mar. 31, 1992) that employ a plurality of complementary outwardly and inwardly projecting regions. A section of such a container is shown in FIGS. 2A-2B. The inwardly projecting regions 13 terminate in closed tips 15 and the outwardly projecting regions 17 each have an opening 19 at its tip such that when roots are guided to the openings, the tips of the roots are dehydrated by exposure to air and effectively air-root pruned, thereby stimulating root branching. These container designs work fairly well, but also exhibit some shortcomings. In particular, it has been observed that numerous roots of a plant disposed in such containers will evade the air-root-pruning openings, in part, because in use the outwardly projecting regions 17 have lower inner surfaces 21 that slope upwardly (i.e., upwardly and outwardly) and are therefore substantially normal to the naturally-occurring paths—outwardly and downwardly—that a large majority of the roots will follow. The root tips encountering such upwardly-sloping surfaces 21 tend to be deflected or ricocheted away from the pruning openings 19.
It is therefore highly desirable that each root of a transplantable plant that would otherwise extend outwardly and contact the sidewall of a plant container be guided to an opening for air-root-pruning and not be allowed to ricochet off the container sidewall and extend down the sidewall or horizontally around the container.
It is further desirable to provide an improved container for growing transplantable plants, whereby spiral and circular root growth is reduced or prevented, and the development of lateral root tips (axially) along and (circumferentially) around the sides of the container is maximized.
It is still further desirable to provide a sheet that is formable into an improved plant growth container wherein the production of lateral root tips is promoted at all levels in a plant growth medium and the root tips quickly grow in all natural directions, whereby the plant is quickly laterally anchored when transplanted and maximum water and nutrients are absorbed.